patch 8.2.3456: Vim9: not all functions are tested with empty string argument

Problem:    Vim9: Not all functions are tested with an empty string argument.
Solution:   Add tests with empty strings. (Yegappan Lakshmanan, closes #8915)
diff --git a/src/version.c b/src/version.c
index 6865fa5..5c4eca6 100644
--- a/src/version.c
+++ b/src/version.c
@@ -758,6 +758,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    3456,
+/**/
     3455,
 /**/
     3454,